Renovators working on Notre Dame cathedral were regularly smoking illegally before the fire that almost destroyed the famous Paris landmark, it has been reported.

Extensive interviews carried out by detectives since last week’s horrific blaze has led to a number of confessions, according to French media.

"In the hearings, some workers admitted that they were smoking on the scaffolding, despite the strict ban," says a shock report in the Canard Enchaine (The Chained Duck), France’s leading investigative news outlet.

Police have also found seven discarded cigarette butts on the scene, the publication adds.

While the cause of the fire is still considered accidental, any proof that a discarded cigarette butt led to the fire could result in a prison sentence.

The flames gutted the roof of the famous cathedral (Image: YOAN VALAT/EPA-EFE/REX)

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The damage was minor, and the fire was easily brought under control by firefighters, but Le Bras restorers were once again implicated, and interviewed by police.

The Paris investigating source said: "The company has accepted responsibility for the fire in Belleville, but not the one in Paris. What happened in Belleville is obviously of significance to the enquiry in Paris."

Le Bras Freres last year finished a widespread restoration programme of Reims Cathedral in eastern France.

It had won the contract to restore the Notre Dame spire that was designed by the architect Eugene Viollet-le-Duc and erected in 1859.

Emmanuel Macron has pledged to rebuiled the famous monument (Image: REUTERS)

They were due to be on site for up to four years along with Europe Scaffolding, another company which had just put 250 tons of scaffolding around Notre Dame, along with a lift that could move up and down the 300ft fire.

Notre Dame has been closed for the foreseeable future, but a trust fund has already raised more than a billion euros for its restoration.

French president Emmanuel Macron has pledged that it will reopen ‘within five years’ and that it will be ‘more beautiful’ than before.